Method for controlling a fuel system of a multiple injection system

ABSTRACT

A method for controlling a fuel system of a multiple injector engine provides a primary fuel injector and a secondary fuel injector which are both connected in fluid communication with an air stream flowing to a combustion chamber of the engine. Based on the total magnitude of fuel required to be injected into the air stream and as a function of the engine speed and percent load of the engine, first and second shares of the total magnitude of fuel are determined for the primary and secondary fuel injectors. The primary and secondary fuel injectors are then caused to inject their respective shares of the total fuel magnitude into the air stream, with the primary and secondary shares being determined as a function of engine speed and percent load of the engine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally related to a supercharging system foran engine and, more particularly, to a supercharged system having twosuperchargers which each provide a share of the fuel based on enginespeed and the load on the engine.

2. Description of the Prior Art

Many different types of supercharger systems are known to those skilledin the art. U.S. Pat. No. 5,937,833, which issued to Kapich on Aug. 17,1999, describes a control system for a hydraulic supercharger system.The control system is specially adapted to control a supercharger systemcomprising a hydraulic pump, a supercharger having a hydraulic turbinedrive and a compressor driven by the hydraulic turbine drive, a mainhydraulic piping means providing a hydraulic circulation loop forhydraulic fluid to flow from the pump to drive the hydraulic turbinedrive and back to the pump, and a supercharger bypass system comprisinga control bypass valve and a piping means to permit a portion of thehydraulic fluid to bypass the supercharger turbine drive. The controlsystem includes a bypass control valve arranged to close and partiallyand fully open the controlled bypass valve. The bypass control valve maybe a hydraulic valve controlled by the pressure of the compressed airintake to the engine. The bypass control valve may also be a solenoidvalve controlled by a pressure switch connected to sense hydraulicpressure and to apply a voltage to the solenoid valve to open or closethe valve upon the hydraulic pressure reaching a predetermined value.

U.S. Pat. No. 5,937,832, which issued to Kapich on Aug. 17, 1999, isgenerally similar to U.S. Pat. No. 5,937,833 which is described above.The control system includes a solenoid arranged to close and partiallyor fully open the control bypass valve. The solenoid may be controlledby a pressure switch connected to sense hydraulic sense and to apply avoltage to the solenoid to open or close the valve upon the hydraulicpressure reaching a predetermined value. Since the hydraulic pressureincreases with engine speed, it is a simple matter to adjust the controlsystem to provide for the hydraulic fluid to drive the supercharger orbypass the supercharger at any predetermined ranges of engine speed. Thebypass valve may also be controlled based on engine throttle position.In another preferred embodiment where the turbocharger system comprisesan air flow check valve which opens when a turbocharger is providing airto the engine, the bypass valve is also subject to control based on theposition on the check valve so that the hydraulic supercharger can besubstantially bypassed when the turbocharger is able to providesufficient air to the engine.

U.S. Pat. No. 5,127,386, which issued to Sowards on Jul. 7, 1992,describes an apparatus for controlling a supercharger. The apparatusincludes a compressor having a rotor portion, an inlet, and a discharge.A motor portion of the apparatus has an intake manifold connected to thedischarge. A throttle is displaceable between an open and closedposition for controlling fluid flow between the discharge and the intakemanifold. A bypass return line connects the rotor portion of thecompressor to the inlet. A piston valve, moveable between an openlocation and a closed location, controls flow through the bypass returnline. A control line, connecting the intake manifold to the piston rodcontrols the location of the piston valve. A control valve may beincluded to control fluid flow through the control line. A computer,which is affected by the operation of the motor, controls the positionof the control valve.

U.S. Pat. No. 4,637,210, which issued to Yamamoto on Jan. 20, 1987,describes a supercharge pressure control apparatus of a superchargedengine. A bypass is provided to bypass a supercharger turbine arrangedbetween the intake and exhaust passages. A waste gate valve is attachedat one end of the bypass and is coupled to an actuator having a pressurechamber communicated with a connecting passage which is branched at abranch point into the first and second passages. A first port is formedin the intake passage downstream near a suction inlet of a compressorand a second port is formed in the intake passage downstream of thefirst port. In the stationary operating state, the connecting passage iscommunicated with the second passage by the charge-over valve, so that ahigh pressure from the second port acts on the pressure chamber and thesupercharged pressure is maintained at a set level. In the accelerationoperating state, the connecting passage is communicated with the firstpassage for a predetermined time, so that a low pressure from the firstport acts on the pressure chamber. When the pressure at the first portoperates the set level, the pressure at the second port exceeds the setlevel, so that a supercharged pressure over the set level is suppliedinto the engine. After a preset time, the connecting passage iscommunicated with the second passage and the pressure is held at the setlevel.

U.S. Pat. No. 4,530,339, which issued to Oguma et al on Jul. 23, 1985,describes a supercharger control apparatus for motor vehicles. Theapparatus comprises a control device which has as input signals thedemand signal for acceleration and an engine rotation speed signal.Based on predetermined ranges of demand signal for acceleration andengine rotational speed and on the input signals, the control deviceregulates, through an actuator and bypass valve or through an actuatorand variable capacity compressor, the amount of supercharging. Thesupercharge control apparatus allows a non-supercharged state, a maximumsupercharged state, or an intermediate supercharged state. In theintermediate supercharged state, the amount of supercharging is inincremental steps to prevent hunting.

U.S. Pat. No. 4,461,149, which issued to Suzuki on Jul. 24, 1984,describes a turbocharger control system for an internal combustionengine. The system comprises a supercharger for applying a superchargepressure to the engine by driving a compressor with a turbine rotated bythe energy of the exhaust gas, and an exhaust gas bypass valve forregulating the amount of the exhaust gas supplied to the turbine. Afactor related to the engine combustion state, such as a knockingcondition, is detected and a signal representing the condition isgenerated. At least one output pressure produced from the compressor ismodified in accordance with the above-mentioned signal. The pressurethus modified is used for adjusting the opening of the exhaust gasbypass valve thereby to control the supercharge pressure.

U.S. Pat. No. 5,848,582, which issued to Ehlers et al on Dec. 15, 1998,discloses an internal combustion engine with barometric pressure relatedstart of air compensation for a fuel injector. The control system for afuel injector system for an internal combustion engine is provided witha method by which the magnitude of the start of air point for theinjector system is modified according to the barometric pressuremeasured in a region surrounding the engine. This offset, ormodification, of the start of air point adjusts the timing of the fuelinjector system to suit different altitudes at which the engine may beoperating.

U.S. Pat. No. 6,032,642, which issued to Trumbower et al on Mar. 7,2000, describes a method for enhanced split injection in internalcombustion engines. It describes a method for controlling fuel deliveryin a fuel injection system capable of performing a split injection andincludes the step of comparing at least one engine operating temperatureto a temperature threshold and disabling split injection when the engineoperating temperature exceeds the temperature threshold. Disabling splitinjection in this manner enhances cold temperature engine operatingwhile providing a single injection at higher operating temperatures, asdesired. Further, an engine and a computer readable storage mediumhaving information stored thereon representing the instructionsexecutable by an engine controller for comparing at least one engineoperating temperature to a temperature threshold are also described. Thecomputer readable storage medium instructions disable split injectionwhen the engine operating temperature exceeds the temperature threshold.

U.S. Pat. No. 5,924,403, which issued to Thomas on Jul. 20, 1999,describes a method for enhanced split injection in internal combustionengines. It describes a method for controlling a compression-ignitioninternal combustion engine which provides a delivery of multiple fuelinjection pulses per cylinder firing with precision of pulse quantities,separation, and timing adequate for transition between split and singleinjection at any speed and load, without disturbing the primary enginegovernor. The method compensates for variable operating conditions suchas supply voltage, injection pressure, injection pulse separation, andinjector actuation latency or rise-time.

U.S. Pat. No. 5,778,858, which issued to Garabedian on Jul. 14, 1998,describes a fuel injection split engine. An automobile includes anengine and an engine controller. The engine includes multiple cylinders.Each cylinder has a fuel injector connected to the engine controller.The engine controller has a first output which activates a firstfraction of the fuel injectors. In addition, the engine controller has asecond output which activates a second fraction of the fuel injectors.The engine controller also has an input which provides a timing signalsynchronous with rotation of the engine and sequencing circuitresponsive to the timing signal. The sequencing circuit periodicallyalternates between the first and second output in synchronization withthe rotation of the engine.

U.S. Pat. No. 5,492,098, which issued to Hafner et al on Feb. 20, 1996,describes an apparatus for variably controlling the fuel flowcharacteristics of a hydraulically actuated injector during an injectioncycle. The apparatus includes variable control of actuating fluidpressure and a spill control apparatus associated with the plunger andbarrel assembly of the injector. The apparatus can control the initialrate of fuel injection and also provide continuous or split injectionthroughout the load and speed range of an engine. Performance iscontrolled by the geometry of the spill control apparatus along with thevariably controlled pressure of the actuating fluid supplied to theinjector. The apparatus helps reduce engine noise and emissions.

U.S. Pat. No. 5,231,962, which issued to Osuka et al on Aug. 3, 1993,describes a fuel injection control system with split fuel injection fora diesel engine. At startup, a fuel injection control system for thediesel engine injects a pre-jet of fuel into a combustion chamber insynchronism with a signal indicative of an angular position of thecrankshaft of the diesel engine. After the pre-jet of fuel has beeninjected, the fuel injection control system injects a main jet of fuelwhich is larger in quantity than the injected pre-jet of fuel. Even whenthe engine rotational speed is low and subjected to variations as atengine startup, the pre-jet of fuel is reliably injected into thecombustion chamber at a desired time. The prejet of fuel which isinjected and ignited prior to the main jet develops an easily ignitable,activated condition in the combustion chamber. The subsequently injectedmain jet of fuel can thus be easily ignited by the activated conditionin the combustion chamber. The diesel engine can be started quickly andsmoothly without fail.

U.S. Pat. No. 4,146,006, which issued to Garabedian on Mar. 27, 1979,describes a fuel injection split engine. A circuit is described for amultiple cylinder engine which permits operation of all of the enginecylinders or part thereof in response to engine loads. Differentoperating modes, incorporating different number of cylinders, areactivated in a fuel injection engine in response to varying powerdemands. Manual switching circuits on the dashboard of the automobilepermit the driver to override the automatic system and require that theengine operate in any of its operating modes. When operating in partialmodes, a circuit automatically rotates the cylinder banks which areoperated to assure uniform engine wear and cooling. Switches areprovided on the dashboard to permit the operator to selectively skipcertain engine modes in the automatic, load-responsive sequencing ofengine operation.

The patents described above are hereby expressly incorporated byreference in the description of the present invention.

It would be significantly beneficial, in view of the superchargersystems known to those skilled in the art, to provide a control methodfor a supercharged engine in which the air charge mass provided to thecombustion chambers of the engine is controlled as a function of chargeair temperature, charge air pressure, and barometric pressure.

SUMMARY OF THE INVENTION

A method for controlling a supercharger, made in accordance with thepresent invention, comprises the steps of disposing the supercharger influid communication within an air stream flowing to a combustion chamberof a cylinder of an engine, selecting a desired magnitude of air percylinder (APC) to be provided to the combustion chamber of the engine,measuring an actual pressure of charge air provided to the cylinder ofthe engine, measuring an actual temperature of charge air provided tothe cylinder of the engine, providing a throttle valve disposed upstreamfrom the supercharger and the combustion chamber for controlling theamount of air flowing to the inlet of the supercharger, through thesupercharger, to the combustion chamber, providing a bypass conduitconnecting the outlet of the supercharger to the inlet of thesupercharger, and providing a bypass valve within the bypass conduit tocontrol the flow of air from the outlet of the supercharger to the inletof the supercharger through the bypass conduit.

The method of the present invention further comprises the steps ofcalculating an actual magnitude of air charge mass provided to thecombustion chamber as a function of the actual charge air temperatureand the actual charge air pressure, determining a difference between theactual magnitude of charge air and the desired magnitude of charge air,and controlling the position of the bypass valve as a function of thedifference between the actual magnitude of charge air and the desiredmagnitude of charge air.

The method of the present invention can further comprise the steps ofmeasuring an actual barometric pressure of the air surrounding theengine and calculating a ratio of the actual charge air pressure to theactual barometric pressure (i.e. “MAP/BARO”). It further comprises thesteps of calculating an actual magnitude of air charge mass provided tothe combustion chamber as a function of the actual charge air pressure,the ratio (i.e. “MAP/BARO”), and the actual charge air temperature.

Certain embodiments of the present invention measure the actual pressureat a location in fluid communication with the charge air between theoutlet of the supercharger and the combustion chamber. The actual chargeair temperature can be measured at a location in fluid communicationwith the charge air between the outlet of the supercharger and thecombustion chamber. A preferred embodiment of the present inventionfurther comprises the step of providing a microprocessor connected insignal communication with the temperature sensor for measuring theactual charge air temperature of air provided to the cylinder and apressure sensor for measuring an actual charge air pressure (i.e. “MAP”)provided to the cylinder, wherein the microprocessor performs thecalculating and determining steps. The calculating step can calculatethe air per cylinder (APC) for the one or more cylinders according to arelationship which defines the air per cylinder as being equal to themanifold absolute pressure (MAP) multiplied by the swept volume of thecylinder and also multiplied by the volumetric efficiency (i.e. {acuteover (η)}) with that product being divided by the product of the idealgas constant R multiplied by the charge air temperature measured withinthe air intake manifold. The engine can be a powerhead of a marinepropulsion system, such as an outboard motor.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully and completely understood froma is reading of the description of the preferred embodiment inconjunction with the drawings, in which:

FIG. 1 is a side view of an outboard motor known to those skilled in theart;

FIG. 2 is a schematic sectional view of the present invention;

FIG. 3 is an illustration of a ten by ten array containing volumetricefficiency values as a function of engine speed and the MAP/BARO ratio;

FIG. 4 is a schematic representation of the method in which a total fuelper cylinder (FPC) is used in combination with a FPC split map; and

FIG. 5 is a graphical representation of how the primary and secondaryshares of the total magnitude of fuel per cylinder (FPC) are changed.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Throughout the description of the preferred embodiment of the presentinvention, like components will be identified by like referencenumerals.

FIG. 1 shows the typical structure of a known outboard motor 2 in whicha cowl 4 is disposed around an engine 10. An output driveshaft 6 of theengine 10 extends downward from the engine 10, through a driveshafthousing 5, and in torque transfer relation with a propeller 7. Thetorque transfer relationship is represented schematically by dashedlines 8 and 9 in FIG. 1. In certain types of engine 10, a superchargercan provide charged air under pressure to the combustion chambers withinthe cylinders of the engine 10.

Although the present invention will be described in greater detail belowin conjunction with a single cylinder, it should be understood that theprinciples of the present invention are intended for use with engineshaving one or more cylinders.

FIG. 2 shows certain portions of an engine 10 in conjunction with thecomponents used to perform the process of the present invention.Represented by dashed lines in FIG. 2, a cylinder 14 is shaped toreceive a piston 16 in sliding relation therein. A valve 18 is moveablewithin an opening 20 to allow a fuel/air mixture to enter the combustionchamber above the piston 16 and within the cylinder 14.

Air is drawn into the system at an inlet 24 of an air intake manifoldand pressurized by a compressor 30 which produces pressurized charge airat an outlet 32 of the compressor 30. This air passes through a throttlevalve 40, which is a butterfly valve in one embodiment of the presentinvention. The throttle valve 40 is controlled by an engine controlmodule (ECM) 44 that provides signals to an actuator 46 which cancomprise a stepper motor, but it should be understood that other typesof actuators 46 can be used. The throttle valve 40 controls the flow ofair through the portion of the intake manifold 50 downstream from thethrottle valve 40.

With continued reference to FIG. 2, a bypass conduit 60 connects theoutlet 32 of the compressor 30 with the inlet 64 of the compressor 30. Abypass valve 70 controls the flow of air through the bypass conduit 60and is controlled by the engine control module (ECM) 44. The enginecontrol module 44 provides control signals to an actuator 74 whichmanipulates the position of the valve 70, which can be a butterflyvalve. As can be seen in FIG. 2, the pressures at the outlet 32 of thecompressor 30 and the region of the intake manifold 50 downstream fromthe supercharger are determined as a combined function of the positionsof the throttle valve 40 and the bypass valve 70.

The engine control module 44 is provided with signals from a pressuresensor 80 and a temperature sensor 82. In addition, another pressuresensor 86 is provided to measure the barometric pressure in the regionsurrounding the engine 10. The engine control module 44 receives theactual manifold absolute pressure, measured by the pressure sensor 80,on line 90, the actual charge air temperature measured by thetemperature sensor 82, on line 92, and the barometric pressure (BARO)measured by the pressure sensor 86, on line 96.

In FIG. 2, the supercharger 30 is disposed in fluid communication withinthe air stream flowing through an intake manifold to a combustionchamber of a cylinder 14 of an engine 10. As will be described ingreater detail below, the engine control module 44 selects a desiredmagnitude of charge air, such as an air per cylinder per cycle magnitude(APC) to be provided to the combustion chamber of the engine 10. Theengine control module 44 then measures an actual pressure on line 90 andan actual temperature on line 92 relating to the air charge massprovided to the cylinder 14. The throttle valve 40 is disposed upstreamfrom the supercharger 30 and the combustion chamber of the cylinder 14for controlling the amount of air flowing to the supercharger 30 and tothe combustion chamber. A bypass conduit 60 is connected between theinlet 64 of the supercharger and the outlet 32 of the supercharger and abypass valve 70 is disposed within the bypass conduit 60 to control theflow of air from the outlet 32 of the supercharger 30 to the inlet 64 ofthe supercharger 30 through the bypass conduit 60. The engine controlmodule calculates an actual magnitude of air provided to the combustionchamber as a function of the actual temperature on line 92 and theactual pressure on line 90 and determines a difference between theactual magnitude of air and the desired magnitude of air. Based on thisdifference, the engine control module (ECM) 44 controls the position ofthe bypass valve 70. If the actual magnitude of charge air is greaterthan the desired magnitude of charged air, the engine control module 44opens the bypass valve 70 to allow a greater amount of air to flowaround the compressor 30 in a reverse direction back to its inlet 64. Ifthe actual magnitude of charged air is less than the desired magnitudeof charged air, the engine control module 44 closes the bypass valve 70by a preselected amount to cause more of the compressed air to flowthrough the throttle valve 40 to the cylinder 14. The actual air percylinder per cycle (APC) of the engine is calculated by the enginecontrol module 44 as a function of the measured actual pressure on line90, the measured actual temperature on line 92, and the barometricpressure on line 96. More specifically, the microprocessor of the enginecontrol module 44 calculates the air per cylinder per cycle according tothe relation shown below.

 APC=(MAP)(Volume)(Volumetric Efficiency)/(R)(Temperature)  (1)

In equation 1, shown above, “MAP” represents the manifold absolutepressure measured by the pressure sensor 80 and provided on line 90 tothe engine control module 44. The cylinder swept volume is apredetermined magnitude that represents the total volume of the cylinder14 swept by the piston 16. The volumetric efficiency is determined as afunction of the engine speed and a ratio (i.e. “MAP/BARO”) between themanifold absolute pressure (MAP) and the barometric pressure (BARO)measured on line 96. The engine speed can be measured by the enginecontrol module directly or, alternatively, by a tachometer 98. Ifmeasured by an external device, such as the tachometer 98, the speed isthen provided to the engine control module 44 on line 99, as shown inFIG. 2.

FIG. 3 represents a two dimensional array that can be stored within amemory of a microprocessor of an engine control module 44. The array canbe a ten-by-ten array in which each of the entries represent avolumetric efficiency ({acute over (η)}) for a particular combination ofengine speed and the ratio between manifold absolute pressure andbarometric pressure. The one hundred element array in FIG. 3 isrepresentative of this type of stored two dimensional array in whicheach of the entries is a volumetric efficiency empirically ortheoretically determined prior to operation of the engine and selectedby the microprocessor of the engine control module 44 as a function ofthe engine speed (i.e. RPM) and the ratio between the manifold absolutepressure and barometric pressure (i.e. “MAP/BARO”). The numerator ofequation 1 is then divided by R, which is the ideal gas constant, andthe inlet air temperature measured on line 92 by the temperature sensor82.

Since equation 1 is a function of all of the pertinent ambientconditions, it implicitly compensates for changes in those ambientconditions, such as temperature, barometric pressure, and actualpressure within the air intake manifold 50. Since the air per cylinderper cycle (APC) is the most direct measure of load in a homogeneouslycharged engine, such as the one described above in conjunction with FIG.2, the methodology of the present invention controls the bypass valve 70according to the most appropriate parameter relevant to a pressurecharged engine.

With continued reference to FIG. 2, a primary fuel injector 100 and asecondary fuel injector 102 are provided to inject fuel into the airstream flowing from the inlet 24 of the intake system to the combustionchamber of the cylinder 14. The primary fuel injector 100 is positionedto direct a spray of fuel vapor toward the intake valve 18. Thesecondary injector 102 is intended to spray fuel into the air stream ata position upstream from the inlet 64 of the compressor 30. The fuelsprayed into the air stream by the secondary fuel injector 102 not onlyprovides fuel that will eventually be combusted within the cylinder 14,but also provides fuel that can cool the compressor 30. During operationof the engine 10, the engine control module 44 provides a total fuelmagnitude value (FPC) to a fuel controller 110. The total fuel magnitudeis determined by any of the known methods used in conjunction with fuelinjected engines. The present invention is not directly related to thespecific technique used to determine the total fuel magnitude valueprovided by the engine control module 44 to the fuel controller 100.However, when two or more fuel injectors are used in a fuel injectedsystem, the present invention provides an efficient way to distributethe fuel commands by the fuel controller 110 to the primary andsecondary fuel injectors, 100 and 102, respectively.

After calculating the total fuel per cycle (FPC) in a manner generallyknown to those skilled in the art, as described in U.S. Pat. No.5,848,582, the present invention uses a two dimensional array to storeone hundred fuel per cycle split values as a function of engine speed(i.e. “RPM”) and percent of load (i.e. “LOAD PERCENT”). Depending on thetype of engine with which the present invention is used, the percent ofload (i.e. “LOAD PERCENT”) can be determined as a function of the fuelper cycle (FPC) in a stratified charge engine or the air per cylinderper cycle (APC) in a homogeneously charged engine. If the control systemused in conjunction with the engine is a torque based system, asdisclosed in U.S. application Ser. No. 09/422,614 which was filed onOct. 21, 1999 by Suhre and assigned to the assignee of the presentapplication, the fuel per cycle (FPC) is determined as a function ofengine speed and torque demand. However, it should be understood thatthe initial determination of the total fuel per cylinder (FPC) is notlimiting to the present invention. After the total fuel per cylindervalue (FPC) is determined, the fuel per cylinder split map 120 is usedto select the percentage of the total fuel per cylinder that will beinjected by the primary injector 100 as shown in FIG. 4. The remainderof the total fuel per cylinder (FPC) will be injected by the secondaryfuel injector 102. For example, if the engine speed and percent loadindicate a magnitude of 0.70 as selected from the appropriate entry ofthe ten-by-ten array 120, 70% of the total fuel per cylinder (FPC) willbe injected by the primary injector 100 and the other 30% of the totalfuel per cylinder (FPC) will be injected by the secondary injector 102.

In a typical application of the present invention, the FPC split map 120shown in FIG. 4 will likely provide magnitudes of 1.00 for the entriesin the ten-by-ten array representing a low engine speed and a low loadpercent (i.e. bottom left comer of array 120). The magnitudes stored inthe array 120 would represent gradually lower values for increasingengine speed and increasing load percent. In other words, at maximumengine speed and maximum load percent, at the upper right portion of theFPC split map 120, the empirically determined entries would typically bein the 0.20 to 0.50 range. This would represent a situation in which theprimary injector 100 is providing between 20% and 50% of the total fuelper cycle (FPC) and the secondary injector 102 is providing theremainder of the fuel. It should be understood that the maximum outputcapability of the primary fuel injector 100 affects the entries in theFPC split map 120 because, at high engine speeds and high percent loads,50% of the total fuel per cylinder (FPC) may hypothetically be themaximum output of the primary fuel injector 100. As the engine speed andthe load per cent increase, the total fuel per cylinder (FPC) alsoincreases. The values stored in the ten-by-ten array 120 represent the“share” of the total fuel per cylinder (FPC) provided by each of the twofuel injectors, 100 and 102 and not the actual amount of fuel.

FIG. 5 illustrates a theoretical time-based graphical representation ofhow the shares of the total magnitude of the fuel per cylinder (FPC) isdynamically changed for the primary and secondary fuel injectors in oneadaptation of the present invention. Beginning at the left portion ofthe graph of FIG. 5, the hypothetical primary fuel injector 100(downstream) share of the total fuel per cylinder (FPC) is representedby line 200 and is equivalent to 80% of the total fuel per cylinder. Theshare of the total fuel per cylinder injected from the secondary fuelinjector 102 (upstream) is represented by line 204 in FIG. 5. It isshown as a 20% share. At some time during the operation of the engine,the secondary fuel injector's share is changed from 20% to 30%, asrepresented by step 206 and line 208 and the primary fuel injector'sshare of the total fuel per cylinder injected through the primary fuelinjector is correspondingly changed from 80% to 70%, as represented byline 210. However, the change in the primary fuel injector's share isnot a step function but, instead, is a ramp 214 as shown. Similarly, ata later time when the secondary fuel injector is decreased in share from30% to 10%, as represented by step 220 in line 224, the primary fuelinjector's share is changed from 70% to 90%, as represented by line 230,in a ramped change as represented by line 234. Although certainembodiments of the present invention can employ step change functionsfor both the primary 100 and secondary 102 fuel injectors, a preferredembodiment changes the primary fuel injector's share of fuel injected bythe primary fuel injector in a ramped method as represented by linesegments 214 and 234 in FIG. 5.

Although the present invention has been described in particular detailand illustrated to show a preferred embodiment, it should be understoodthat alternative embodiments are also within its scope.

We claim:
 1. A method for controlling a fuel system of a multipleinjector engine, comprising s the steps of: providing a primary fuelinjector in fluid communication with an air stream flowing to acombustion chamber of said engine for injecting fuel into said airstream; providing a secondary fuel injector in fluid communication withsaid air stream flowing to a combustion chamber of said engine forinjecting fuel into said air stream; determining a magnitude of totalfuel per cylinder to be injected into said air stream; measuring a speedof said engine; determining a percent load of said engine; selecting afirst share of said magnitude of total fuel per cylinder to be injectedinto said air stream by said primary fuel injector and a second share ofsaid magnitude of total fuel per cylinder to be injected into said airstream by said secondary fuel injector, both as a combined function ofboth said speed of said engine and said percent load of said engine;causing said primary fuel injector to inject said first share of saidmagnitude of total fuel per cylinder to be injected into said airstream; and causing said secondary fuel injector to inject said secondshare of said magnitude of total fuel per cylinder to be injected intosaid air stream, said magnitude of total fuel per cylinder to beinjected into said air stream being equal to the sum of said first andsecond shares.
 2. The method of claim 1, further comprising: providing asupercharger in fluid communication with said combustion chamber.
 3. Themethod of claim 2, wherein: said primary fuel injector is disposed influid communication with said air stream between said supercharger andsaid combustion chamber.
 4. The method of claim 2, wherein: saidsupercharger is disposed in fluid communication with said air streambetween said primary and secondary fuel injectors.
 5. The method ofclaim 1, wherein: said first share is selected from a two dimensionalarray of first share values.
 6. The method of claim 1, wherein: saidsecond share is calculated as the difference between unity and saidfirst share.
 7. A method for controlling a fuel system of a multipleinjector engine, comprising the steps of: providing a primary fuelinjector in fluid communication with an air stream flowing to acombustion chamber of said engine for injecting fuel into said airstream; providing a secondary fuel injector in fluid communication withsaid air stream flowing to a combustion chamber of said engine forinjecting fuel into said air stream; determining a magnitude of totalfuel per cylinder to be injected into said air stream; measuring a speedof said engine; determining a percent load of said engine; selecting afirst share of said magnitude of total fuel per cylinder to be injectedinto said air stream by said primary fuel injector and a second share ofsaid magnitude of total fuel per cylinder to be injected into said airstream by said secondary fuel injector, both as a combined function ofboth said speed of said engine and said percent load of said engine;providing a supercharger in fluid communication with said combustionchamber, said primary fuel injector is disposed in fluid communicationwith said air stream between said supercharger and said combustionchamber; causing said primary fuel injector to inject said first shareof said magnitude of total fuel per cylinder to be injected into saidair stream; and causing said secondary fuel injector to inject saidsecond share of said magnitude of total fuel per cylinder to be injectedinto said air stream, said magnitude of total fuel per cylinder to beinjected into said air stream being equal to the sum of said first andsecond shares.
 8. The method of claim 7, wherein: said supercharger isdisposed in fluid communication with said air stream between saidprimary and secondary fuel injectors.
 9. The method of claim 8, wherein:said first share is selected from a two dimensional array of first sharevalues.
 10. The method of claim 9, wherein: said second share iscalculated as the difference between unity and said first share.
 11. Amethod for controlling a fuel system of a multiple injector engine,comprising the steps of: providing a primary fuel injector in fluidcommunication with an air stream flowing to a combustion chamber of saidengine for injecting fuel into said air stream; providing a secondaryfuel injector in fluid communication with said air stream flowing to acombustion chamber of said engine for injecting fuel into said airstream; determining a magnitude of total fuel per cylinder to beinjected into said air stream; measuring a speed of said engine;determining a percent load of said engine; selecting a first share ofsaid magnitude of total fuel per cylinder to be injected into said airstream by said primary fuel injector and a second share of saidmagnitude of total fuel per cylinder to be injected into said air streamby said secondary fuel injector, both as a combined function of bothsaid speed of said engine and said percent load of said engine, saidsecond share being calculated as the difference between unity and saidfirst share; providing a supercharger in fluid communication with saidcombustion chamber, said primary fuel injector is disposed in fluidcommunication with said air stream between said supercharger and saidcombustion chamber; causing said primary fuel injector to inject saidfirst share of said magnitude of total fuel per cylinder to be injectedinto said air stream; and causing said secondary fuel injector to injectsaid second share of said magnitude of total fuel per cylinder to beinjected into said air stream, said magnitude of total fuel per cylinderto be injected into said air stream being equal to the sum of said firstand second shares.
 12. The method of claim 11, wherein: saidsupercharger is disposed in fluid communication with said air streambetween said primary and secondary fuel injectors.
 13. The method ofclaim 12, wherein: said first share is selected from a two dimensionalarray of first share values.